Modern internal combustion engines often use Hall effect or optical sensors that provide engine ignition timing information to an engine control unit (ECU). The use of a programmable ECU can allow modification of the engine characteristics, which is typically used to increase performance or efficiency. Older engines may have a less sophisticated or less full-featured ECU. Upgrading an ECU can be an excellent after-market route to increase performance of an engine, however, this can be difficult when the sensors and other inputs from an older engine are not compatible with the expected inputs for the new ECU. This is a particular issue with older engines that use a different distributor system and engine position signals.
For example, General Motor's (GM) LT series engines (sometimes referred to as Gen 2 or LT Family) came with a factory installed Optispark distributor. Inside the Optispark is an optical sensor and a timing disc which has two rows of notches. The first row contains 360 evenly spaced notches, the second row has 8 notches of different sizes to indicate certain cylinder position. This optical sensor and disc are what makes up the “opti” in “Optispark”. The second system at work in the Optispark, the “spark” portion, is a more traditional rotor and cap distributor which distributes high tension spark to the engines spark plugs. The LT series engine's ECU used the information from the Optispark's optical sensor and timing disc to know where all the cylinders are in terms of precise engine angular rotation. Knowing the exact engine position, the LT Gen 2 ECU would then calculate and electronically tell the Optispark when to fire the high tension leads.
After the LT engines, GM developed the LS series engines (sometimes referred to as Gen 3 or LS Family). On LS series engines GM decided to do away with a rotor and cap distributor (and the problems that accompanied the Optispark design) and use a coil-per-cylinder ignition system. The optical sensor and timing disc of the Optispark were replaced with the LS series engine's new system of detecting accurate angular engine position. This new position system used a crankshaft reluctor and camshaft reluctor. The crankshaft reluctor in conjunction with a corresponding sensor produces 24 unique pulses per 360 degrees of engine rotation that the Gen 3 ECU interprets to determine engine position. For this reason, this crankshaft position signal is often referred to as the “24× signal”. Similarly, the camshaft reluctor and associated sensor provides what is called the “1× signal” because it is either on for 180 degrees of camshaft rotation or off for 180 degrees of camshaft rotation. The 1× signal allows the ECU to know whether a given cylinder is on its firing stroke or intake stroke; an important piece of information due to the fact that the 24× crankshaft reluctor rotates twice per complete engine cycle. The 24× signal and 1× signal are illustrated in FIG. 7.
In order to use a Gen 3 ECU on a Gen 2 GM engine, the Gen 2 engine needs to generate the appropriate 24× crankshaft signal and 1× camshaft signal, and these signals needed to be routed to the correct input of the Gen 3 ECU. The 24× and 1× signals must be generated reliably and also accurately read by the sensors in order for the ECU to know the precise engine position. Prior art approaches to modifying these Gen 2 engines for Gen 3 ECUs is costly and labor intensive.
One known approach to modifying Gen 2 engines to produce the 24× crankshaft signal and 1× camshaft signal requires removing the engine timing cover. An exploded view of a replacement timing cover that uses this methodology is illustrated in FIG. 1. Installation requires removing the timing cover (and obstructing components). Next, the camshaft reluctor 12 and crankshaft reluctor 14 are attached to the corresponding shafts on the engine. Timing cover 10 is then reinstalled on the engine block. Timing cover 10 includes a port 16 for receiving a crank Hall effect sensor 18. A cam Hall effect sensor 20 is included on additional cover 22 that when attached to timing cover 10 positions cam Hall effect sensor 20 near camshaft reluctor 12.
Another disadvantage of the design shown in FIG. 1 is that it also difficult to adjust the relative positions of camshaft and crankshaft reluctors to the corresponding sensor because the reluctors are enclosed within the timing cover. This can make it difficult to obtain proper alignment between reluctors and the corresponding sensor.